25 September 2009

David Keith on Air Capture

Air capture is an industrial process that captures CO2 from ambient air, producing a pure CO2 stream for use or disposal . . . Near-term development of air capture only makes sense if it can be realized at a sufficiently low cost. . . Air capture is neither a silver bullet nor a hopeless dream: It is simply another chemical engineering technology. Disputes about cost can only be resolved by developing a few air capture technologies to the point where they can be independently evaluated. Costs cannot be understood until specific processes are developed to a far greater technical depth than has been achieved to date. As with other energy technologies, it is not possible to determine the cost through small-scale university research alone. Instead, costs will only become evident with pilot-scale process development and when costing can be performed by contract engineering firms with relevant expertise.

Remarkably, Keith asserts that:

There are no government funding programs that specifically target the development of air capture, and I estimate that the total annual expenditure for these efforts is currently less than $3 million per year, of which more than half is private.

He argues why there should be such a program of investment:

A more substantial investment of government R&D funding is warranted for at least three reasons. First, early estimates suggest that air capture will be competitive with technologies that are getting large R&D investments. For example, the cost of cutting CO2 emissions by displacing carbon-intensive electricity production with roof-mounted solar photovoltaic panels can easily exceed $500 per ton of CO2. Yet even skeptics (10) suggest that a straightforward combination of existing process technologies could probably achieve air capture at lower cost. And the fact that several groups have raised private money for commercialization suggests that there are investors who believe that it is possible to develop technologies to capture CO2 from air at costs closer to $100 than $500 per ton of CO2.

Second, air capture offers one route to make carbon-neutral hydrocarbon fuels (CNHCs) for vehicles by using captured CO2 to make synthetic fuels. Deep reductions in emissions from the transportation sector will require a change in vehicle fuel. Each of the three leading alternative fuel options—electricity, biofuels, and hydrogen—faces technical and economic hurdles that preclude major near-term reductions in transportation emissions. CNHCs represent a fourth, fundamentally different alternative: a method for converting primary energy from carbon-free sources such as solar or nuclear power into high–energy-density vehicle fuels compatible with the current vehicle fleet. It is unclear whether CNHCs will be competitive with the three leading alternatives, but they are promising enough to warrant R&D support on a par with efforts aimed at advancing the alternatives (20). Finally, air capture allows negative global CO2 emissions. Although this is a distant prospect, it is important because it represents one of the few ways to remediate human impact on the carbon cycle, an impact that is otherwise all but irreversible.

I have emailed David to ask if his cost numbers should be in terms C not CO2. Even so, as written the costs are squarely in the middle of the range that I discussed in my recent paper on air capture:

Air capture may or may not contribute to efforts to stabilize greenhouse gas concentrations. But so long as scientists and policy makers frame climate policy as in terms of stabilizing concentrations of atmospheric carbon dioxide, then given current indications of its potential effectiveness and cost, air capture deserves to be among the options receiving attention in the international climate policy debate.